The present invention relates to a highly elastic breathable film laminate made by a vacuum forming lamination process. The resulting laminate is useful in disposable products such as diapers and hygiene products.
Various processes for bonding thermoplastic films to non-woven webs or other thermoplastic films are known. The present invention is an improvement over the current state of the art non-woven laminate films. The assignee herein, Tredegar Industries is a leader in developing both non-woven/film laminated composites and formed three-dimensional film technology. For example, the Raley U.S. Pat. No. 4,317,792 relates to a formed three-dimensional film and the method for making such a film. In addition, the Merz U.S. Pat. No. 4,995,930 relates to a method for laminating a non-woven material to a non-elastic film.
Various types of formed elastic films and processes for making these films are known. The Wu U.S. Pat. No. 5,422,172 proposed an elastic laminate formed by incremental stretching of the web. However, the resulting the film has a 10% permanent set after 50% elongation which is considered to be a low performance elastic material. Further, the vapor or air permeability of the product is achieved by providing mechanical microvoids.
The Swenson et al. U.S. Pat. Nos. 5,462,708; 5,422,178; and 5,376,430 discloses elastic film laminates having an elastic core layer and at least one polymeric skin layer. However, these films are non-breathable films. There is no suggestion of utilizing a non-woven material as a skin contact layer. Further, the processes of the Swenson et al. patents would require additional materials and processing steps in order to utilize a breathable non-woven material.
The Hodgson et al. U.S. Pat. No. 5,304,078 discloses a method for forming a heat shrinkable film that exhibits elastic properties only after being shrunk. The product produced by the ""078 patent is not breathable and does not utilize a non-woven composite material.
The Knight U.S. Pat. No. 5,336,554 discloses a porous elastomeric film wherein air permeability is provided by the use of laser perforation. The ""554 patent proposed a high cost manufacturing process in order to achieve breathability for elastic films and laminates.
The Mitchell et al. U.S. Pat. Nos. 5,068,138 and 4,970,259 disclose the use of blown film to produce a of non-breathable elastomeric films. The ""138 and the ""259 patents do not address, handle or process the inherently tacky elastomeric film. Further neither patent suggested laminating the elastomeric film to a non-woven material.
There is considerable difficulty in working with and processing elastomeric films to form useful products. The inherent tacky and stretchy characteristics of elastomeric films make the films extremely difficult to process. It is especially difficult to use any elastomeric film as a layer in a multilayer laminate.
The present invention addresses those concerns discussed above. The inherently tacky nature of elastomeric film compositions makes the films difficult to use. For example, in hygiene products, only a small piece of the stretchy material might be used. The steps of removing the film from a roll or festoon, cutting the film to size, and moving the cut film are all hindered by the films"" tendency to stick to the processing equipment. The prior art required the use of non-tacky thermoplastic skin layers in order to handle the elastic film in further processing steps.
Further, as products with greater elasticity are used in medical and hygiene applications, skin care issues increase. The more stretchable elastic products conform better to the body so breathability from around any loose fitting perimeter of the product is greatly reduced. The closer fit of the elastic product decreases the air flow to the skin, thus increasing the tendency for the skin to remain undesirably moist.
There is still a continuing need for improved elastic film laminates. It is desirable to provide an elastic film laminate which can be readily incorporated into a finished product without the use of adhesive materials or other additional processing steps. It is also desirable to further improve the elastic films by making the elastomeric films breathable or vapor permeable. The elastic breathable laminate films are useful in disposable products and the like where skin irritation is a concern.
The present invention overcomes the drawbacks described above and provides a breathable and elastomeric laminate comprising an elastomeric film laminated to a non-woven material. The breathable elastomeric laminate of the present invention is formed in a single processing step without the need for additional adhesive materials.
The present invention relates to a highly elastic breathable film laminate comprising a three-dimensional elastomeric film layer and a carrier or support web layer. It is to be understood that the terms xe2x80x9celasticxe2x80x9d and xe2x80x9celastomericxe2x80x9d can be used interchangeably, and that both terms are within the contemplated scope of the present invention. These terms, xe2x80x9celasticxe2x80x9d and xe2x80x9celastomericxe2x80x9d, relate to materials which are stretchable under force and are recoverable as to the material""s original or essentially original form upon release of the extension force.
The carrier material provides the desired mechanical properties needed for handling of the elastic film laminate and for conversion of the laminate to a finished product. In various embodiments, the carrier web can comprise a thermoplastic film material or a fibrous material. The fibrous material can comprise a fibrous web, woven and/or non-woven materials.
The high stretch, elastomeric film laminate of the present invention combines the advantages of elasticity as well as breathability. It is contemplated that the high stretch elastic film laminate of the present invention can be incorporated as a layer in various types of end use products. The resulting elastic film laminate is useful for disposable products, such as side panels in diapers and hygiene products, and for medical applications, such as wound dressings and bandages.
According to one embodiment of the present invention, a predetermined thickness of a layer of a carrier material is introduced onto a top surface of an elastomeric film material just prior to or directly at the point of forming the three-dimensional characteristics of the film. The carrier material is supplied under an appropriate tension to the film material. In preferred embodiments, the elastic film is formed into a three-dimensional structure using a vacuum or pressure differential process. The carrier material covers a predetermined area of the elastomeric film surface and partially embeds or fuses onto the top surface of the elastomeric film material.
A preferred embodiment of the present invention comprises a film laminate wherein the carrier layer comprises a fibrous material. In certain embodiments, the fibrous material comprises non-woven materials, while in other embodiments the fibrous material can comprise woven or loose fibers. One advantage of the present invention is that a uniform layer of fibrous material can be applied to an elastic film during the film making process. Until the present invention, it has not be possible to supply a layer of fibrous material onto an elastic three-dimensional, apertured film to allow the film laminate being formed to retain its elastomeric characteristics.
In the embodiments where the carrier material comprises a fibrous material, the resulting film has the aesthetic appeal of cloth-like fabrics. Further, the film has the dryness aspects of three-dimensional formed films which is desirable in such end uses as disposable products and wound dressing or bandages.
According to preferred embodiments of the present invention, the thermal energies of both the molten or semi-molten polymeric elastomeric film material and the carrier material are precisely controlled at the point in time when the elastomeric film is subjected to a pressure differential for forming the three-dimensional structure of the film. The thermal energies of the film material and carrier material are controlled such that the heat transfer (which is required to achieve the bond between the elastomeric film material and the carrier material) does not detract from the ability of the elastomeric film material to be further formed into its three-dimensional structure.
In embodiments where the carrier material comprises a fibrous material, portions of the fibrous material become embedded in, or fuse into or onto, the top surface of the film without distortion or loss of the integrity of the fiber. The fibrous material embeds or fuses onto the top surface of the elastomeric film as the three-dimensional structure of the film is being formed such that a fibrous coated three-dimensional apertured elastic film laminate is produced. The resulting film laminate has high stretch or elongation in the cross direction and good breathability characteristics and increased aesthetic value.
In certain embodiments, the relative positions of the film extrusion die and the point of lamination of the film material and carrier material are varied to achieve the bond strengths needed to laminate the carrier material and the elastomeric film material together while maintaining the elastic properties of the film material. The precise location or impingement point at which the carrier material is delivered onto the top surface of the molten or semi-molten elastomeric film material can occur prior to or subsequent to the formation of the three-dimensional structure of the film. In various embodiments, the carrier material is delivered onto the top surface of the molten or semi-molten elastomeric film material at a point in time prior to the three-dimensional structure of the film being formed. In another embodiment, a layer of the carrier material is melt bonded to a top surface of the molten or semi-molten elastic film material at a point in time after the formation of the three-dimensional characteristics of the elastic film.
In a preferred embodiment, the precise location or impingement point of carrier material-to-film material is chosen such that various operating conditions are met. The contact temperature and contact pressure between the carrier material and the elastomeric film material are regulated. The location of the impingement of the carrier material onto the elastomeric film material is regulated such that the carrier material does not touch the molten or semi-molten elastomeric film material prematurely, but only at a desired impingement point.
In a preferred embodiments, the impingement point is located at a predetermined distance from the point at which the pressure differential is supplied to the bottom surface of the elastomeric film material. The carrier material is delivered onto the top of the elastomeric film material without interfering with the formation of the three-dimensional structures being formed in the film material. The pressure differential is regulated such that the three-dimensional structures are apertured such that the elastic film laminate is breathable.
The carrier material supplies additional resistance to the fluid or air displacement across the pressure differential. As the elastomeric film/carrier material laminate passes across the pressure differential, the amount of pressure differential is regulated to compensate for the additional resistance resulting from the presence of the carrier material laminated to the top surface of the elastomeric film material. In a preferred embodiment, the carrier material is supplied onto the elastomeric film material in a manner such that there is minimal, if any, obstruction or resistance to air flow or to the pressure differential being used to form the three-dimensional structures in the film material.
In preferred embodiments, the three-dimensional structures being formed are expanded protuberances or apertures in the elastomeric film. Thereafter, sufficient heat is removed to a point below the temperature of solidification or hardening temperature of the material before the elastomeric film material/carrier material laminate is removed from the pressure differential.
The present invention can be practiced using a batch process using premade rolls of carrier material such as fibrous web materials and/or film-type carrier materials. The present invention can also be practiced using a continuous supply of carrier material such as individual fibers or fibrous webs introduced onto the film material. The present invention can further be practiced using a continuous supply of a film of the carrier material which is co-extruded or introduced onto the elastomeric film material. In certain other embodiments, the carrier material can be supplied onto the elastomeric film material to form a laminate which is apertured in a secondary process.
It is further within the completed scope of the present invention that the elastic film laminate of the present invention can comprise a multilayer structure comprising a first layer of a carrier material, a layer of a elastomeric, three-dimensional film material, and a third layer of a carrier material.
In certain preferred embodiments, the carrier material comprises less than about 40% of the effective thickness of the combined elastomeric film/carrier material laminate. In certain other embodiments, the carrier material can be sufficiently thick to provide an additional function such as cloth-like characteristics and/or absorbent or liquid acquisition and transmission properties to the elastic film laminate. In other embodiments, the carrier material is sufficient thin to mainly provide separation of the stretchy elastomeric film from the processing equipment both during the processing and the end use applications of the film (i.e., when the elastic film laminate is being incorporated into a finished product).
In certain embodiments, the carrier material comprises a film that exhibits low to moderate levels of elasticity such as polyethylene, polypropylene, ethylene vinyl acetate and other such polymeric materials. It is to be understood that the carrier material can include other ingredients such as anti-block and anti-slip ingredients. It is further understood that the carrier material can comprise more than one layer and that the carrier material can be a co-extruded film material. Each layer of the co-extruded carrier material can have different properties which enhance the lamination of the carrier material to the elastomeric film and/or provide other advantages to the laminate film.
In certain embodiments where the carrier material comprises a fibrous material, it is within contemplated scope of the present that the fibrous materials can include polyesters, polyolefins, acrylics, rayons, cottons and other cellulose materials, and blends of the same. The fibrous materials can also include bi-component fibers having an inner core of one material and an outer core of a second material, adhesive fibers, as well as fibrous materials having fibers of different geometries, lengths, diameters and surface finishes. The fibrous material can comprise loose fibers, woven materials and non-woven materials which have different basis weights, fiber compositions, fiber lengths, and which can be made using different processes.
In certain embodiments, the elastomeric film material can comprise a material which is considered highly stretchable and which reverts to its original or nearly original form upon release of any pressure or force applied to the film material. Elastomeric materials which are useful in the present invention include polyolefin type materials such as polyethylene elastomers, and polyurethane films. In preferred embodiments, the preferred elastomeric film material is capable of achieving essentially fully recovery after being stretched at least about 300 to about 400% of its original length. Suitable stretchable elastomeric films comprise natural polymeric materials and synthetic polymeric materials including isoprenes, butadiene-styrene materials and other elastomers. Other suitable elastomers comprise styrene block copolymers such as styrene/isoprene/styrene (SIS), styrene/butadiene/styrene (SBS), or styrene/ethylene-butadiene/styrene (SEBS) block copolymers. Blends of these polymers alone or with other modifying elastic or non-elastomeric materials are also contemplated being useful with the present invention. In certain preferred embodiments, the elastomeric materials can comprise such high performance elastomeric material such as Kraton(copyright) elastomeric resins from the Shell Chemical Co., which are elastomeric block copolymers.